The present invention relates to radio transceivers having multiple voice and data input/output channels, and in particular to radio frequency power control algorithm for dynamically sharing among the channel transmitters of the available output power.
Mobile cellular to satellite communication system radio transceivers having multiple voice and data input/output channels are known. One example of such a mobile cellular to satellite communication system is the AIRSAT(copyright) Multi-Channel Satellite Communication System, described in a brochure published October 1997 by AlliedSignal Incorporated, entitled xe2x80x9cAIRSAT MULTI-CHANNEL SATELLITE COMMUNICATION SYSTEM for IRIDIUM(copyright),xe2x80x9d which provides worldwide continuous multichannel voice and data communications for commercial air transport aircraft. Such mobile cellular to satellite communication systems accept data and voice from various sources onboard the aircraft, encode and modulate this information to appropriate Radio Frequency (RF) carrier frequencies, and transmit these carriers to the satellite constellation for relay to the ground. Mobile cellular to satellite communication systems also receive RF signals from the satellite constellation, demodulate these signals, perform the necessary decoding of the encoded messages, and output data or voice for use onboard the aircraft by crew members and passengers.
FIG. 1 illustrates a block diagram of the avionics forming a specific implementation of the airborne mobile cellular to satellite communication (SatCom) systems equipment 100 of a satellite communication system, which provides worldwide continuous multi-channel voice and data communications for commercial air transport aircraft. Airborne SatCom equipment 100 accepts data and voice input from various sources onboard the aircraft, encodes and modulates this information to appropriate radio frequency (RF) carrier frequencies, and transmits these carriers to the satellite constellation for relay to the ground. The avionics also receives RF signals from the satellite constellation, demodulates these RF signals, performs the necessary decoding of the encoded messages, and outputs data or voice for use on-board the aircraft by crew members and passengers.
The avionics forming one typical implementation of mobile cellular to SatCom equipment 100 for commercial air transport aircraft include, for example, a satellite terminal or telecommunications unit (STU) 102; cavity filter/low noise amplifier (CF/LNA) package 104; a high power amplifier (HPA) 106; and a low gain antenna (ANT) 108. According to at least one implementation of mobile cellular to SatCom equipment 100 for commercial air transport aircraft, each of the avionics are fully compliant with ARINC Characteristic 761, Second Generation Aviation Satellite Communication System, and ARINC Characteristic 746, Cabin Communications System.
In FIG. 1, mobile cellular to SatCom equipment 100 resident on multiple aircraft includes, for example, satellite terminal or telecommunications unit 102, which is essentially a mobile switch, allowing several users, including passengers, flight crew and automated avionics systems, to share the radio channel units (RCUs) 110 contained within satellite telecommunications unit 102. Radio channel units 110 are modular radio units which typically support both voice and data transmissions on the L-Band radio frequency link, including such standard mobile cellular telephone capabilities as voice mail, call forwarding and worldwide messaging, PC data, packet data, and facsimile transmissions, as defined by GSM, the mobile cellular network found throughout Europe, Africa, Asia, and Australia defining the standards governing wireless networks in those territories. A typical satellite telecommunications unit 102 also supports multiple ARINC 429 interface channels. One specific implementation currently provides 7 communication channels: 3 voice channels and 4 data channels. Specific proprietary implementations of satellite telecommunications unit 102 support multiple external interfaces, including, for example, Conference Europeene des Postes et Telecommunications (CEPT-E1) interface to cabin telecommunications unit (CTU) 112 communicating using ARINC Characteristic 746 protocol over a over a high speed serial bus pair interface, which can accommodate multiple digitized voice channels along with status and control information.
Cabin telecommunications unit 112 interfaces with the cabin/passenger telecommunication equipment 114, such as telephone handsets 116 and data ports 118 via in integrated services digital network (ISDN). Cabin telecommunications unit 112 supplies the traditional private branch exchange (PBX) features for the cabin/passenger telecommunication equipment. Cabin telecommunications unit 112 also functions to provide signal processing, i.e., analog-to-digital and digital-to-analog conversion; dial tone generation; call queuing; and providing status messages, such as, xe2x80x9cPlease hold; your call is being processed.xe2x80x9d
Cavity filter/low noise amplifier (CF/LNA) package 104 includes cavity filter (CF) 120 and either a low noise amplifier (LNA) or a diplexer low noise amplifier (DLNA) 122, depending upon the specific embodiment. Cavity filter (CF) 120 and low noise amplifier 104 switch the transmit (TX) and receive (RX) paths to low gain antenna 108 from satellite telecommunications unit 102. Low gain antenna 108 also amplifies the receive signal to the level required by satellite telecommunications unit 102. Cavity filter/low noise amplifier circuit 104 insures that the transmit path is isolated from the receive path during the transmit mode to prevent damage to sensitive low noise amplifier 122. High power amplifier 106 receives and amplifies the combined transmitter output power of all active radio channel units 110 and transmits the amplified signals to antenna 108 for transmission to a satellite network for communication. High power amplifier 106 preferably provides an sufficient RF power level to antenna 108 to maintain the aircraft Effective Isolation Radiated Power (EIRP) within specified limits. The design of high power amplifier 106 generally accounts for varying cable losses and avoid excessive thermal dissipation. Antenna 108 is preferably a weight, size and cost-conscious low profile, low gain antenna that provides adequate link margins from all reasonable aircraft orientations and satellite orbits.
The total fixed power level capability of high power amplifier 106 is divided into multiple radio channel units 110. Each radio channel unit 110 includes a transmitter (not shown) that transmits at a fixed power level depending upon the type of communication, voice or data, assigned to an individual radio channel unit 110. FIG. 1 shows a typical division of radio channel units 110 into four voice channels and three data channels. A processor portion of satellite telecommunication unit 102 directs the various voice communications on handsets 116 to one of the four voice radio channel units and directs data communications on data ports 118 to one of the three data radio channel units. As mentioned above, radio channel units 110 are each permanently assigned as either voice or data channels and preset to appropriate output power levels. Both voice and data channels are preset to an appropriate initial output power level, where this initial output power level is determined according to the system requirements necessary to maintain a particular minimum bit error rate (BER) in the specific voice or data link. Voice data can typically tolerate an overall higher BER than can an equivalent data link and remain useful, i.e. intelligible. The overall BER is a function of the power in the channel. Therefore, the initial power level on the data channels is typically higher than on the voice channels to maintain an acceptable BER. Output power is fixed for each voice and data channel and cannot be shared among different radio channel units 110. Lower output power voice signals can be transmitted using data channels, but data transmissions are limited to using only the higher power data channels. Because output power cannot be shared among different radio channel units 110, power from inactive voice channels cannot be added together into a single voice channel to perform data transmissions, thus limiting mobile cellular to SatCom system 100 to a fixed number of data channels. Higher output power data channels can be used to transmit voice, but the output power available to an unused voice channel cannot be diverted to an active voice channel.
Transceivers in such mobile cellular to satellite communication systems include a high power amplifier providing a fixed power output level capability divided into the multiple voice and data input/output channels. While the number of available data and voice channels depends upon the manufacturer""s implementation, the available channels are divided into a fixed number of data channels and fixed number of voice channels, each preset to specific output power levels. The power levels for each of the voice and data channels are separate. While the power levels needed for voice and data channels are based on the specific implementation, voice channels require less output power than data channels. Voice transmissions are confined to the human audible frequency range. In contrast, data transmissions, such as facsimile and computer modem transmissions, cover a wider frequency range and, thus, require more output power. Voice transmission, requiring less output power, can be transmitted using the data channels, but data transmissions are limited to using only the higher output power data channels. Nor can power from unused voice channels be added together into a single voice channel to perform data transmissions. Furthermore, the fixed power output capability of the high power amplifier limits the number of transmission channels. Therefore, the mobile cellular to satellite communication system is limited to a preset total number of transmission channels, including a preset number of channels for data transmissions. Although voice can be transmitted using data channels, additional output power in an inactive voice or data channel cannot be diverted to an active voice channel to, for example, increase the volume of the on-going voice transmission.
What is needed is a means for determining the total output power available without violating the integrity of the high power amplifier and dynamically varying the output power available to each channel, such that power usage is optimized.
The present invention overcomes the limitations of the prior art by providing a multichannel mobile cellular to satellite communication system wherein each channel transmitter dynamically changes its output power based on a message from a control processor. The control processor tracks the number and type of all active calls and adjusts the output power of each channel transmitter to limit the high powered amplifier output power to a range that will not violate its integrity.
According to one aspect of the present invention, a method is provided for dynamically adjusting the radio frequency (RF) output power level in each channel transmitter of a multichannel mobile cellular to satellite telecommunication system having multiple communication devices, such as telephone handsets and data ports, each associated with a different input channel of the multichannel mobile cellular to satellite telecommunication system.
According to one aspect of the present invention, a RF power control algorithm operating on a microprocessor monitors each of several input channels to detect a call request from one of the communication devices. The RF power control algorithm of the invention tracks the activity on each of the channel transmitters via multiple input channels associated with different ones of the transmission channels of the multichannel mobile cellular to satellite telecommunication system. When a call request from one of the communication devices is detected on one of the input channels, the invention determines the availability of the transmission channels and assigns the call to an available one. Preferably, the invention determines the type of call requested, i.e., voice or data, and then calculates adjusted output power parameters for each of the transmission channels. The invention transmits a message containing the parameters to each transmission channel. In response to the parameters in the messages, the satellite telecommunication system dynamically adjusts the output power of each transmission channel.
According to another aspect of the invention, the RF power control algorithm calculates the adjusted output power parameters for each of the transmission channels as a function of the number of active data and voice transmission channels, the minimum power required for each call type based on an allowable bit error rate, and a maximum safe output power of the high power amplifier, whereby the combined adjusted output power of the active transmission channels will not violate its integrity.
According to another aspect of the invention, the availability of ones of the transmission channels is determined either by comparing the number of currently active transmission channels against the maximum number of transmission channels, or by surveying the different channels. If no transmission channel is available, the invention transmits a negative reply to the requesting communication device. However, if a transmission channel is available, the invention automatically initiates a call.
According to still another aspect of the invention, the invention provides a system for dynamically adjusting the output power level in each voice and data transmission channel of a multichannel mobile cellular to satellite telecommunication system. The system of the invention has a memory for storing multiple machine instructions and a processor coupled to the memory and executing the machine instructions to implement multiple functions. The processor includes multiple input and output channels, the input channels associated with different ones of the communication devices, and the output channels associated with different ones of the transmission channels. The functions at least include: receiving a call request signal from communication equipment on one of the processor""s input channels; assigning the call to one of the available voice and data transmission channels; calculating new output power parameters for each transmission channel; and transmitting a message containing the new parameters to each transmission channel associated with one of the output channels. The mobile cellular to satellite telecommunication system dynamically adjusts the output power of each transmission channel in response to the new transmitted parameters.